Communication networks must be capable of transporting extremely large amounts of information having different formats (e.g., voice, video, data, and so on) and at the highest speeds possible. As a result, flexible bandwidth management and efficient transmission protocols are essential elements in any network solution. Recent advances in communication technologies have assisted service providers in meeting the increasing demands being placed on today's networks. For example, optical fiber is fast becoming a transmission medium of choice for many communication networks because of the speed and bandwidth advantages associated with optical transmission. In addition, wavelength division multiplexing (WDM) is being used to obtain even more bandwidth and speed in today's optical transmission systems. In its simplest form, WDM is a technique whereby parallel data streams modulating light at different wavelengths are coupled simultaneously into the same optical fiber. By using optical transmission and WDM in the backbone networks, the communications industry has made great strides in terms of solving the bandwidth and speed problems.
However, an efficient transport protocol for carrying the various types of traffic across these optical communication networks continues to be an elusive problem. Although the type of traffic being transported or being planned for transport over these networks continues to evolve, one constant is that future networks need to be capable of carrying a mix of several traffic types in an efficient, flexible, and scalable manner. In general, the type of traffic transported in the networks can be characterized in two categories, mono-media whereby only one type of session is supported, and multimedia, whereby a session can be composed of multiple mono-media sessions. The former case is comparable to traditional circuit or packet networks where voice, data, or video sessions are established and traffic is carried. In the current Internet, early versions of multimedia sessions are observed. For example, upon gaining access to a server, an end user is permitted to access video and audio clips, exchange data, as well as establish real-time connections such as voice and video. Presently, two of the most common types of transport protocols are Asynchronous Transfer Mode (ATM) and Transmission Control Protocol/Internet Protocol (TCP/IP), referred hereinafter as IP. To capitalize on the benefits offered by ATM and IP, coupled with the many advantages associated with optical transmission, a great deal of effort is being applied to develop the most efficient manner for transporting ATM and IP traffic across today's optical communication networks.
Most existing optical transmission networks are based on the well-known Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) standard. Because the differences and similarities between SONET and SDH are well known, examples described hereinafter will only refer to SONET for simplicity of explanation. A common approach in today's networks is to use a SONET-based system for transporting the different types of traffic. For example, in SONET-based transport, information is formatted according to specified byte and frame structures in the electronic domain and then converted to optical format for transport as a serial bit stream over a lightwave communication system. In WDM, each wavelength channel therefore may carry such formatted traffic, but in parallel so that capacity significantly increases. One proposed approach for supporting the different traffic types) e.g., ATM and IP, is to use the standard SONET frame structure for carrying the ATM cells or IP packets. Although SONET transport has many advantages, SONET is not viewed as a long-term solution to optical communication networks which must support a mix of traffic types.
For example, SONET does not provide an explicit routing process at the cross-connects and/or switches/routers. SONET also does not provide a signaling capability for path setup between source/destination end devices for which communications should take place, e.g., application layer. Furthermore, in order to extract information from SONET payload, complex processing using embedded pointers in its path and section headers is required. With respect to carrying multiple traffic types, the SONET frame structure was not originally designed to handle ATM cells and IP packets and, as such, is not optimized for transmission of such formats.
Cost is also a significant factor in terms of supporting the addition of future services. In particular, a solution for transporting multiple traffic types should not require revamping the existing infrastructure. Future networks need to be transparent to the type of traffic being carried and new traffic types should be accommodated with, at most, minor modifications at the interface to the network infrastructure. Furthermore, capacity should be capable of being managed based on actual traffic demand, e.g., incrementally add or remove capacity.